Integrated circuits have increasing been made at higher integration levels. For the production of semiconductor substrates for super LSI and the like, it is now required to fabricate ultra super fine patterns of a line width of quarter-micron or less. As one of approaches for making such super fine patterns, a method has been known for modifying the wavelength of exposure light sources for use in resist patterning into shorter wavelength.
For the production of a semiconductor device up to an integration level of 64 megabits, so far, the i beam (365 nm) from high pressure mercury arc lamp has been used as a light source. Numerous compositions including novolak resin and naphthoquinone diazide compounds as photosensitive materials have been developed for the positive resist corresponding to the light source and have successfully achieved great results in the processing of a line width of about 0.3 μm. For the production of a semiconductor device at an integration level up to 256 megabits or more, further, KrF excimer laser (248 nm) in place of the i beam has been used as an exposure light source.
For the purpose of producing semiconductor at an integration level of 1 gigabits or more, still further, the use of ArF excimer laser (193 nm) as a light source of shorter wavelength together with the use of F2 excimer laser (157 nm) for the fabrication of patterns of 0.1 μm or less has been investigated recently.
Following the modification of the wavelengths of these light sources into shorter wavelength, constituent components of resist materials and the structures of such compounds have been changed dramatically.
As a resist composition for exposure to KrF excimer laser, so called chemical amplification resist has now been developed, where a resin with the essential backbone poly(hydroxystyrene) with small absorption in the 248-nm zone, as protected with acid decomposable groups, is used as the main ingredient, in combination with compounds generating acids under irradiation of far ultraviolet ray (optical acid generators).
Further, resists of chemical amplification type have been developed as resist compositions for exposure to ArF excimer laser (193 nm) alike, where acid decomposable resin with an alicylic structure with no absorption at 193 nm is introduced in the main chain or side chain of a polymer.
It is revealed that even the alicylic type resin has such large absorption in a region around 157 nm for F2 excimer laser beam (157 nm) that the alicyclic type resin is unsatisfactory for obtaining an intended pattern of 0.1 μm or less. In contrast, Proc. SPIE., Vol. 3678, p. 13 (1999) reports that a resin introduced with fluorine atom (perfluoro structure) has sufficient transparency at 157 nm, while the structures of the effective fluorine resins are proposed in Proc. SPIE., Vol. 3999, p. 330 (2000); ibid., p. 357 (2000); ibid., p. 365 (2000); and WO-00/17712. Resist compositions containing fluorine-containing resins have been investigated so far.
Additionally, J. Photopolym. Sci. Technol., Vol. 15, No. 4, p. 643 discloses a resin for exposure to F2 excimer laser beam, which is prepared by copolymerization of vinyl sulfonate with a styrene monomer with fluorine atom.
However, these resists cannot satisfactorily exert various performances such as transparency at 157 nm, sensitivity, resolution, contact potency to developers and the like.
Further, resist compositions of related art, which contain fluorine resins for exposure to F2 excimer laser beam, are problematic in terms of line edge roughness, development defects, development residue (scum) and the like. Therefore, it has been desired that these problems may be overcome.
The term “line edge roughness” means that the edge in the interface between the line pattern on resist and the substrate is in shapes irregularly deforming along the direction vertical to the line direction, which is ascribed to the characteristic profile of the resist. When the pattern is observed directly overhead, it is observed that the edge has protrusions and recesses (in about ± several nm to several tens nm). Because the protrusions and recesses are transferred onto the substrate at the etching process, the protrusions and recesses when they are large cause poor electric properties, leading to the reduction of the yield.